We have focused our attention on the role of insulin-like growth factors (IGF's) and tumor specific translocations in the pathogenesis of pediatric sarcomas specifically rhabdomyosarcomas (RMS), osteogenicsarcoma (OS), and Ewing's sarcomas/PNET (Ewing's family of tumors EFT). We have continued to study the role of Loss of imprinting (LOI) of IGF-II in RMS as contributing to overexpression. We have found that the P2, P3, and P4 promoters are all relaxed in RMS with LOI. Of note, however we have recently found that 3/10 ES tumor specimens informative at the IGF-II locus have LOI of IGF-II and in this case LOI does not lead to overexpression of IGF-II suggesting that LOI may be a general finding in various tumors and represent an epigenetic alteration in tumors not directly related to IGF-II per se. We have also begun to study transcriptional regulation of IGF-II. We have found that PAX-3/FKHR fusion protein created by the ARMS specific t(2;13)(q35;ql4) markedly up regulates transcription from the IGF-II P3 and P4 promoter in transient reporter gene assays. Furthermore, wild-type p53 has been found to inhibit TBP binding to the P3 TATA region leading to transcriptional inhibition, while mutant p53 has lost this activity. We have also found that the HIV transcriptional factor tat can increase IGF-II P3 and P4 transcriptional activity, suggesting a potential mechanism leading to increased incidence of leiomyosarcoma in HIV infection of children (leiomyosarcomas overexpress IGF-II). We have continued to explore the role of IGF's in osteosarcoma and have demonstrated that a noncalcitropic Vit D analog inhibits growth and induces differentiation in a human OS cell line, and this is associated with a dramatic increase in IGFBP-3 levels, although IGFBP-3 alone has no activity. We have also been studying structure/function relationships of the IGF- I receptor and we are currently examining the ability of a dominant negative receptor mutation to inhibit the growth of rhabdomyosarcomas engrafts in nude mice. We have recently developed in vitro and in vivo models to study the ability to develop cytotoxic T Lymphocytes directed specifically against tumor specific translocation derived fusion proteins in rhabdomyosarcoma and Ewing's sarcoma.